This invention relates to a control method for a moisture meter, a control program for a moisture meter, a recording medium recording a control program for a moisture meter and a moisture meter and it is applicable particularly to the heating dry type moisture meter. According to the invention, the heating temperature is sequentially raised gradually to detect a parameter of a time function indicating the change of moisture percentage, and according to the parameter, the optimum heating temperature is calculated, or the required mass of a sample is calculated from the measurement accuracy set by an operator and the measurement accuracy of the mass, whereby a condition for measurement can be set simply and surely.
In the heating dry type moisture meter, the moisture percentage of a sample has been detected by heating moisture to evaporate and measuring the change of mass heretofore. That is, when the mass of the sample before starting such heating (hereinafter referred to as mass before drying) is taken as W, and the mass of the sample after drying is taken as D, the moisture percentage WP of the sample can be expressed by the following formula.[Formula 1]                    WP        =                                            W              -              D                        W                    ×                      100            ⁢                                                  [            %            ]                                              (        1        )            
Thus, in the heating dry type moisture meter, when the quantity of a sample is large, the measurement accuracy is improved for that, but it takes much time for drying, resulting in lengthening the measurement time. Therefore, in the conventional moisture meter, when the required accuracy is taken as X[%] and the measurement accuracy of weight in the moisture meter is taken as M[g], the calculation on N=M/X is performed by an operator to find the mass N of the sample. According to this, the measurement accuracy of weight is 1 [mg], and in the case of calculating the moisture percentage with the accuracy of 0.01%, the quantity of the sample is 10 [g].
In the heating dry type moisture meter, when the heating temperature is elevated, moisture can be evaporated in a short time, whereby the time required for measurement can be reduced. When the heating temperature becomes high, however, liquid (e.g. volatile oil or the like) other than moisture contained in the sample volatilizes and decomposes, and when the temperature becomes further higher, an organic matter contained in the sample is carbonized to thereby deteriorate the measurement accuracy.
Thus, in the conventional moisture meter, heating conditions are set by a preliminary test in advance. Here the heating conditions are the time for drying a sample by heating (the heating time), the heating temperature, the elapsed time from the start of heating until the temperature is raised to the heating temperature (the temperature rising time), and the like.
That is, in the preliminary test, a sample is heated at a fixed temperature for a predetermined time, and it is detected whether the mass of the sample is changed by evaporation of moisture or not. The heating in the preliminary test is performed at a temperature of 120° C. or the like for ten minutes. In the case where the mass of the sample continues to change even in heating at such a fixed temperature for a fixed time, the heating temperature is varied until finally the mass of the sample is not changed, or at the heating temperature, the heating time is prolonged.
In the preliminary test, a plurality of samples are prepared, the heating temperature, the heating time and the temperature rising time are variously changed to dry the samples, and according to the test results, the heating conditions determined to be suitable are set.
That is, in the moisture percentage measurement using the conventional moisture meter, the thus obtained heating conditions are set on the moisture meter, and then a quantity of sample, which is found by the calculation, is placed. After that, when the measurement is started, in the moisture meter, the mass of the sample before drying is detected and recorded, and heating for the sample is started on the conditions set by a user. After that, the mass in the course of drying is monitored, and according to the monitoring result, the result of measurement still in progress on the moisture percentage is displayed by arithmetic processing of the formula (1). When the heating time elapses, heating is ended, and the measurement result is displayed.
In thus setting the heating conditions through the preliminary test, however, there is a problem that the conditions can't be set simply and surely.
That is, as described above, in the preliminary test, it is necessary to prepare a plurality of samples and heat the same repeatedly, resulting in the problem that it takes long time to make a measurement.
Sometimes even a volatile constituent is evaporated so that the mass of the sample is not changed, and there is the fear that such a case is mistaken as the case where the mass of the sample is not changed due to evaporation of moisture to set the heating conditions. It is considered that the thus set conditions are not suitable. By the way, in the conventional heating dry meter, it requires skill to set the heating conditions.
As described above, it requires a long time to measure each of the plurality of samples, so in the plurality of samples, it is necessary to keep the moisture percentage from being changed for a long time by preventing evaporation of moisture until the measurement is started. Accordingly, in order to maintain and manage such moisture percentage, the maintenance of measurement environment becomes large-scale. Further, the preliminary test becomes complicated, and the complicated work is one main cause of wrong measurement of moisture percentage.